/**
 * Software License, Version 1.0
 * 
 * Copyright 2003 The Trustees of Indiana University.  All rights reserved.
 * 
 *
 *Redistribution and use in source and binary forms, with or without 
 *modification, are permitted provided that the following conditions are met:
 *
 *1) All redistributions of source code must retain the above copyright notice,
 * the list of authors in the original source code, this list of conditions and
 * the disclaimer listed in this license;
 *2) All redistributions in binary form must reproduce the above copyright 
 * notice, this list of conditions and the disclaimer listed in this license in
 * the documentation and/or other materials provided with the distribution;
 *3) Any documentation included with all redistributions must include the 
 * following acknowledgement:
 *
 *"This product includes software developed by the Community Grids Lab. For 
 * further information contact the Community Grids Lab at 
 * http://communitygrids.iu.edu/."
 *
 * Alternatively, this acknowledgement may appear in the software itself, and 
 * wherever such third-party acknowledgments normally appear.
 * 
 *4) The name Indiana University or Community Grids Lab or NaradaBrokering, 
 * shall not be used to endorse or promote products derived from this software 
 * without prior written permission from Indiana University.  For written 
 * permission, please contact the Advanced Research and Technology Institute 
 * ("ARTI") at 351 West 10th Street, Indianapolis, Indiana 46202.
 *5) Products derived from this software may not be called NaradaBrokering, 
 * nor may Indiana University or Community Grids Lab or NaradaBrokering appear
 * in their name, without prior written permission of ARTI.
 * 
 *
 * Indiana University provides no reassurances that the source code provided 
 * does not infringe the patent or any other intellectual property rights of 
 * any other entity.  Indiana University disclaims any liability to any 
 * recipient for claims brought by any other entity based on infringement of 
 * intellectual property rights or otherwise.  
 *
 *LICENSEE UNDERSTANDS THAT SOFTWARE IS PROVIDED "AS IS" FOR WHICH NO 
 *WARRANTIES AS TO CAPABILITIES OR ACCURACY ARE MADE. INDIANA UNIVERSITY GIVES
 *NO WARRANTIES AND MAKES NO REPRESENTATION THAT SOFTWARE IS FREE OF 
 *INFRINGEMENT OF THIRD PARTY PATENT, COPYRIGHT, OR OTHER PROPRIETARY RIGHTS. 
 *INDIANA UNIVERSITY MAKES NO WARRANTIES THAT SOFTWARE IS FREE FROM "BUGS", 
 *"VIRUSES", "TROJAN HORSES", "TRAP DOORS", "WORMS", OR OTHER HARMFUL CODE.  
 *LICENSEE ASSUMES THE ENTIRE RISK AS TO THE PERFORMANCE OF SOFTWARE AND/OR 
 *ASSOCIATED MATERIALS, AND TO THE PERFORMANCE AND VALIDITY OF INFORMATION 
 *GENERATED USING SOFTWARE.
 */
package cgl.narada.event.impl;

import java.util.Hashtable;

import cgl.narada.event.EventID;

/**
 * This class is responsible for generating identifiers
 * 
 * @author Shrideep Pallickara $Date$ $Revision$
 */

public class EventIDGenerator {

    Hashtable managedEntities;

    private int numOfEntities = 0;

    private int firstEntityId = 0;

    private EntityWidget firstWidget;

    public EventIDGenerator() {
        managedEntities = new Hashtable();
    }

    public synchronized EventID generateEventId(int entityId) {
        if (managedEntities.size() == 0) {
            numOfEntities++;
            firstEntityId = entityId;
            firstWidget = new EntityWidget(entityId);
            managedEntities.put(new Integer(entityId), firstWidget);
            return firstWidget.generateEventId();
        }

        if (entityId == firstEntityId) {
            return firstWidget.generateEventId();
        }

        Integer key = new Integer(entityId);

        /**
         * If this entity is one of several managed by this generator, retrieve
         * the widget and generate the Id.
         */
        if (managedEntities.containsKey(key)) {
            EntityWidget _entityWidget = (EntityWidget) managedEntities
                .get(key);
            return _entityWidget.generateEventId();
        }

        EntityWidget _newWidget = new EntityWidget(entityId);
        managedEntities.put(new Integer(entityId), _newWidget);
        return _newWidget.generateEventId();
    }

    /**
     * The Entity Widget is responsible for generating ID's in a consistent
     * manner
     */
    class EntityWidget {
        int entityId;

        long timestamp;

        int seqNum;

        public EntityWidget(int entityId) {
            this.entityId = entityId;
            reset();
        }

        public EventID generateEventId() {
            if (seqNum == Integer.MAX_VALUE) {
                reset();
            }
            seqNum++;
            return new EventID(entityId, timestamp, seqNum);
        }

        /** Reset the timestamp and sequence number */
        private void reset() {
            timestamp = System.currentTimeMillis();
            seqNum = 0;
        }
    }

    public static void main(String[] args) {
        EventIDGenerator gen = new EventIDGenerator();
        System.out.println(gen.generateEventId(124));
        System.out.println(gen.generateEventId(124));
        System.out.println(gen.generateEventId(124));
        System.out.println(gen.generateEventId(125));
        System.out.println(gen.generateEventId(125));
        System.out.println(gen.generateEventId(124));
        System.out.println(gen.generateEventId(125));
        System.out.println(gen.generateEventId(126));
        System.out.println(gen.generateEventId(124));
    }
}
